Methods of generating magnetic particles in a subterranean environment

ABSTRACT

The subject disclosure relates to methods of generating magnetic particles in a wellbore. More particularly, the subject disclosure relates to a fluid system which comprises two or more fluids which react chemically to generate magnetic particles in a wellbore.

FIELD OF THE DISCLOSURE

This subject disclosure is generally related to magnetic particles, and more particularly to methods of generating magnetic particles in a subterranean environment.

BACKGROUND OF THE DISCLOSURE

Magnetorheological materials are typically comprised of magnetizable particles in suspension in a fluid carrier. A magnetorheological material characteristically exhibits rapid and reversible changes in rheological properties which can be controlled by the application of a magnetic field. The shear stress and viscosity of such a material are related to whether the material is in the presence of a magnetic field, termed the on-state, or in the absence of a magnetic field, termed the off-state. In the on-state, the magnetizable particles align with the magnetic field and substantially increase the shear yield stress and viscosity of the material over its off-state value. Substantial changes in fluid properties via the application of magnetic fields make possible the use of magnetorheological fluids in many industrial applications.

Commonly, state-of-the-art magnetorheological (MR) fluids are multiphase materials consisting of magnetizable particles suspended in a liquid carrier fluid. In the off-state MR fluid exhibits properties typical of a dense suspension. In addition to the magnetizable particles, the carrier fluid serves as a continuous non-magnetic material. Some of the carrier fluids typically utilized are silicone and hydrocarbon oils. An additional component that is often present in MR fluids is a stabilizer, which serves to keep the particles suspended in the fluid.

Magnetorheological fluids present some drawbacks for wellbore applications; several are briefly described in the following section. The use of magnetorheological fluids in long and vertical fluid columns (e.g. within a conduit) such as those found in wellbores can cause problems because the fluid density is usually greater than that of the well fluids; thus the magnetorheological fluid may sink before being actuated at a predetermined depth. The introduction of field-responsive fluids in a long column can cause significant differential pressure at wellbore depths because of their high density, thus making the deployment of such fluid over great lengths difficult. Another drawback, presented by such fluids arises from the magnetic nature of the suspended particles. Prior to deploying into a well, oilfield tubulars (e.g. pipes, coupling stocks, etc) are commonly magnetic particle inspected (MPI) to ascertain the absence of surface and shallow subsurface defects that could jeopardize structural integrity. This technique of inspection may lead to remnant magnetization thus attracting magnetic particles creating an issue for delivery of magnetic particles downhole. Finally, the fluid cost may also be prohibitive for economic operations in high fluid volume applications.

It would be desirable to provide a simple means of generating magnetic particles downhole and to use the generated magnetic particles in downhole applications.

SUMMARY OF THE DISCLOSURE

This summary is provided to introduce a selection of concepts that are further described below in the detailed description. This summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended to be used as an aid in limiting the scope of the claimed subject matter.

In view of the above, there is a need for mechanisms for generating magnetic particles in a wellbore for magnetorheological fluid applications. The subject technology accomplishes this and other objectives.

According to some embodiments, systems and methods are described for generating magnetic particles in a wellbore. The method includes introducing a fluid system into the wellbore comprising a first fluid and a second fluid; and reacting chemically the first fluid and the second fluid in the wellbore to form a plurality of magnetic particles.

According to some other embodiments, a process for producing a plurality of magnetic particles is described. The process includes introducing a fluid system into a wellbore comprising a first fluid and a second fluid, reacting chemically the first fluid and the second fluid in the wellbore and co-precipitating a plurality of magnetic particles from said chemical reaction.

It should be appreciated that the present technology can be implemented and utilized in numerous ways, including without limitation as a process, an apparatus, a system, a device, a method for applications now known and later developed. These and other unique features of the system disclosed herein will become more readily apparent from the following description and the accompanying drawings.

BRIEF DESCRIPTION OF THE FIGURES

The subject disclosure is further described in the detailed description which follows, in reference to the noted plurality of drawings by way of non-limiting examples of embodiments of the subject disclosure, in which like reference numerals represent similar parts throughout the several views of the drawings, and wherein:

FIG. 1 illustrates a wellsite system in which the subject disclosure can be deployed;

FIG. 2 illustrates the fluid of FIG. 1 in greater detail;

FIG. 3 illustrates one embodiment of a method of preparing magnetic particles;

FIG. 4A-4C illustrates magnetorheological fluid modes of operation;

FIG. 5 illustrates a magnetorheological fluid valve;

FIG. 6 illustrates a flow chart of one method of the present disclosure; and

FIG. 7 is a diagram, partially in block form, of a logging apparatus of a type that can be used in practicing embodiments of the subject disclosure.

DETAILED DESCRIPTION

The particulars shown herein are by way of example and for purposes of illustrative discussion of the embodiments of the subject disclosure only and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the subject disclosure. In this regard, no attempt is made to show structural details of the subject disclosure in more detail than is necessary for the fundamental understanding of the subject disclosure, the description taken with the drawings making apparent to those skilled in the art how the several forms of the subject disclosure may be embodied in practice. Further, like reference numbers and designations in the various drawings indicate like elements.

The subject disclosure is directed to mechanisms of generating magnetic particles downhole. More particularly, the subject disclosure is directed to mechanisms of generating magnetic particles downhole for subsequent use within a controlled magnetic field. These generated magnetic particles can be used in many downhole applications. In some non-limiting examples magnetic particles are used in sensing and flow control applications. In sensing applications, the magnetic properties of the particles can be used in obtaining a signature in a subterranean environment. The presence of magnetic particles increases the effective magnetic permeability of the medium that contains them. Because of this shift in magnetic properties, the distribution of a static magnetic field and the propagation of the electromagnetic waves will be altered. Therefore, a logging sensor which is sensitive to static magnetic fields or electromagnetic waves may be used to detect the presence of generated magnetic particles. In some applications, the particles generated in the downhole environment effectively convert the fluid that suspends them into a magnetorheological fluid. The size of the generated particles may vary from nanometer sized particles to micron sized particles or larger but other particle sizes are contemplated based on wellbore conditions. Magnetorheological fluids are typically comprised of a suspension of micrometer-sized magnetic particles. In a non-limiting example magnetorheological fluids comprise 20-40% by volume of micrometer sized particles. Magnetic particles in non-limiting examples may be spherical, ellipsoidal or possibly have a shape similar to fibers. The particles are suspended in a carrier fluid, such as mineral oil, water or silicone oil. A higher volume fraction of magnetic particles typically results in a greater viscosity change due to a larger density of magnetic interactions. Water and oils of varying viscosities are commonly used as carriers which are both found in a downhole environment. Under normal conditions, magnetorheological fluids have flow characteristics similar to that of conventional oil. However, in the presence of a magnetic field, the particles become magnetically polarized and organized into chains of particles within the fluid. FIG. 1 illustrates a wellsite system in which embodiments of the subject disclosure can be disposed. Referring to FIG. 1, methods and systems are described for the purposes of delivering fluid systems downhole in a well. More specifically, FIG. 1 depicts an embodiment 101 that may be used to deliver fluid systems inside a wellbore 109 in accordance with embodiments of the subject disclosure. The wellbore 109 may be (as an example) a lateral wellbore that extends through a particular formation 119. In one non-limiting example, the fluid system comprises a first fluid system and a second fluid system. The first fluid system and the second fluid system in a non-limiting example are non-magnetic fluids. In one non-limiting example the first fluid system is a cement slurry. It may be desirable to place cement in an annular region (herein called the “zone of interest” 111) that surrounds a slotted liner 117. Further, it may be desirable to generate magnetic particles for use in downhole applications in the vicinity of the zone of interest 111. For example, a flow control device may be used to allow fluid to enter the string 105. This flow control device may be controlled using the generated magnetic particles. For this purpose, FIG. 1 depicts the use of a tubular string 105 (a coiled tubing string, for example), which extends downhole into the wellbore 109 and is positioned so that its lower end 115 is in proximity to the zone of interest 111. The string 105 is used to deliver the fluid system downhole through its central passageway. As described below, the fluid system comprises a first fluid and a second fluid which mix downhole for purposes of generating magnetic particles. It is noted that the system 101 as depicted in FIG. 1 is merely illustrative, i.e. other systems are also contemplated for the downhole generation of magnetic particles.

Throughout the specification, a material is referred to as magnetic if the said material includes or comprises a substance in which strong magnetic interactions are taking place, for example ferromagnetic, ferrimagnetic or superparamagnetic. On the other hand, a material is referred to as non-magnetic if the strong magnetic interaction is absent. Examples of such material behavior fall into the well-known categories such as diamagnetic or paramagnetic.

Referring again to FIG. 1, the string 105 includes an annular packer 113 that, (when set as shown in FIG. 1) forms an annular seal between the exterior surface of the string 105 and the interior surface of the slotted liner 117. Thus, for the state of the packer 113 depicted in FIG. 1, communication uphole is prevented between the liner 117 and string 105. As also shown in FIG. 1, initial state, a plug, such as a bridge plug 121, may be placed downhole of the end 115 of the string 105 to seal off the central passageway of the slotted liner 117.

FIG. 2 illustrates operation of the generated magnetic particles in a fluid (205) within a conduit (203), in one non-limiting example, the slotted liner 117. The fluid (205) is a magnetorheological fluid including generated magnetic particles (207) suspended in a base fluid (205). An additive may also be included to assist in suspending the particles and preventing agglomeration. In the absence of a magnetic field the magnetorheological fluid behaves similar to a Newtonian fluid. However, in the presence of magnetic field (201) the generated particles (207) suspended in the base fluid (205) reversibly align and form chains which are roughly parallel to the magnetic lines of flux associated with the magnetic field. When activated in this manner by a magnetic field, the magnetorheological fluid is in a semi-solid state which exhibits increased resistance to shear in the form of flow or relative motion between fluid boundaries. In particular, resistance to shear is increased due to the magnetic attraction between the particles of the chains. Fluid viscosity is greatly increased and in certain cases the magnetorheological fluid is comparable to a viscoelastic solid. One important aspect of magnetorheological fluids is that yield stress of the magnetorheological fluid in the presence of a magnetic field can be controlled very accurately by varying the magnetic field intensity. The magnetorheological fluids ability to transmit force can be controlled with a magnetic field, therefore, giving rise to the use of magnetorheological fluids in many control based applications.

The chains of particles act to increase the fluid shear strength or flow resistance of the fluid. When the magnetic field is removed, the particles can return to an unorganized state due to the removal of interparticular magnetic interactions and the fluid shear strength or flow resistance of the fluid returns to its previous value. Thus, the controlled application of a magnetic field allows the fluid shear strength or flow resistance of a magnetorheological fluid to be altered very rapidly.

FIG. 3 depicts a schematic illustration of an embodiment of the subject disclosure. A fluid system comprising a first fluid and a second fluid are introduced into a wellbore. In one non-limiting example both the first fluid and the second fluid are non-magnetic fluids. The first fluid and the second fluid chemically react to produce ferrofluids or magnetic particles (Fe₃O₄). The synthesis is based on reacting iron (II) and iron (iii) ions in an aqueous basic solution to from magnetite, Fe₃O₄ as shown in equation 1.

Fe²+(aq)+2Fe³⁺(aq)+8OH-(aq)

Fe₃0₄(s)+4H₂0(1)  (1)

In non-limiting examples, the first fluid or the second fluid may be a fluid which is used for another function in a wellbore environment. In one non-limiting example, this may be a cement slurry for use in sealing an annular region. Typically, hydraulic cements, particularly Portland cements, are used to cement the well casing within the wellbore. Hydraulic cements are cements which set and develop compressive strength due to the occurrence of a hydration reaction which allows them to set or cure under water. The cement slurry is allowed to set and harden to hold the casing in place. The cement also provides zonal isolation of the subsurface formations and helps to prevent erosion of the wellbore.

In other non-limiting examples the first fluid or the second fluid comprises a strong base, for example, an alkali metal hydroxide. Examples include sodium hydroxide, potassium hydroxide, barium hydroxide, strontium hydroxide, calcium hydroxide, lithium hydroxide, rubidium hydroxide, caesium hydroxide or ammonium hydroxide or combinations thereof. However, these are non-limiting examples, and many other strong bases may be used.

In non-limiting examples, the first fluid or the second fluid may comprise iron ions which include iron (II) hydrated salt and iron (III) salt. In some aspects, the iron (II) salt is iron (II) chloride tetrahydrate, iron (II) sulfate heptahydrate, iron (II) sulfate hydrate, iron (II) oxalate dehydrate, or a combination thereof. However, these are non-limiting examples, and many other iron (II) hydrated salts may be used.

In some aspects, the iron (III) salt is iron (III) chloride hexahydrate, iron (III) nitrate nonahydrate, iron (III) sulfate, iron (III) oxalate hexahydrate, or a combination thereof. However, these are non-limiting examples, and many other iron (III) hydrated salts may be used.

The first fluid and the second fluid reacts chemically producing magnetic particles. The chemical reaction may be co-precipitation which is a convenient way to synthesize iron oxides (either Fe₃O₄ or γ-Fe₂O₃) from aqueous Fe²⁺/Fe³⁺ salt solutions by the addition of a base. Co-precipitation occurs with the addition of sodium hydroxide or ammonium hydroxide. The size, shape, and composition of the magnetic nanoparticles depends on the type of salts used (e.g. chlorides, sulfates, nitrates), the Fe²⁺/Fe₃₊ ratio, the reaction temperature and pressure, the pH value and ionic strength of the media. Applications of the generated particles include flow control and sensing.

Embodiments of the subject disclosure may generate any type of magnetic particle and these magnetic particles may be in any shape and in any fraction for mixtures of magnetic particles. In embodiments of the subject disclosure once the particles have been generated in the desired location they may be used as components of a magnetorheological fluid downhole system functioning in applications downhole.

Embodiments of the subject disclosure may be pumped down through the tubing, or alternatively released into the well under the influence of gravity and flow induced forces.

Once the magnetic particles are generated, a portion of the well fluid, particularly the fluid located close to the apparatus, exhibits magnetorheological properties. Magnetorhelogical fluids can be used in three modes of operation, namely flow mode, shear mode and squeeze mode. FIG. 4A-C illustrates the three major types of modes which utilize magnetorheological fluid properties. FIG. 4A illustrates a flow mode 403 where the shear stress is applied by forcing the magnetorheological fluid 414 through a channel 413. In the flow mode the magnetically formed chains of particles act as a plug to fluid flow through a fluid channel, effectively becoming a magnetic valve. FIG. 4B illustrates a shear mode 407 where the fluid is sheared by tangential relative motion 405 of fluid boundaries. FIG. 4C illustrates a squeeze mode 409 where magnetic particles resist normal relative motion 411 of fluid boundaries. In the shear and squeeze modes of operation, the magnetic chains are used to control the resistance to motion between two or more components. Common examples where these modes are utilized are in magnetorheological clutches, brakes or squeeze film dampers. The magnetic field necessary to modify the magnetorheological fluid behavior can be generated by for example, an electromagnetic coil. The magnetic field may also be present in the wellbore e.g. a permanently magnetized element.

FIG. 5 illustrates an example of a magnetorheological fluid device 505 operating in a flow mode by magnetic fields 509 generated by an electromagnetic coil 511. The device 505 which is a magnetorheological valve comprises a housing 513 and a core 503. The magnetorheological valve comprises a valve intake 501 and a valve discharge 507. When electrical current is present in the coil 511, a magnetic field 509 is generated. Magnetorheological fluid flowing through the device 505 exerts an additional resistance to flow in the presence of a magnetic field 509. When there is no net electrical current flowing through the coil, the magnetic field within the device 505 is effectively zero, neglecting remanant magnetization of the components. The magnetorheological fluid flow occurs with less resistance when the magnetic field is not present.

FIG. 6 illustrates one method of the subject disclosure. A fluid system comprising two or a plurality of fluids is introduced into the wellbore (601). The fluid system is delivered to a certain location in the wellbore. Once the fluid system reaches its destination the fluids chemically react (603) generating magnetic particles (605). Once the magnetic particles are generated they transform the surrounding fluid into magnetorheological fluid (607).

The generated magnetic particles may be used for a variety of applications downhole. More particularly, the subject disclosure may be used in many downhole applications where fluid controllability or sensing is achieved by using magnetic fields. In particular, the generated magnetic particles may be used for sensing or flow control applications.

FIG. 7 depicts one embodiment in which the generated magnetic particles may be utilized. FIG. 7 shows a borehole (707) that has been drilled in a formation (713). A logging device (711) is shown, and can be used in practicing embodiments of the subject disclosure. The device or tool (711) is suspended in the borehole (707) on a cable (709), the length of which substantially determines the depth of the device (711). Known depth gauge apparatus (not shown) is provided to measure cable displacement over a sheave wheel (not shown) and thus the depth of logging device (711) in the borehole (707). Circuitry (705), shown at the surface although portions thereof may typically be downhole, represents control and communication circuitry for the investigating apparatus. Also shown at the surface are processor (701) and recorder (703). The tool (711) can represent any type of logging device that takes measurements from which formation characteristics can be determined, and, for example, may have been determined in the past by solving complex inverse problems. For example, without limitation, the logging device may be an electrical type of logging device (including devices such as resistivity, induction, and electromagnetic propagation devices), a nuclear logging device, a sonic logging device, or a fluid sampling logging device, as well as combinations of these and other devices. Devices may be combined in a tool string and/or used during separate logging runs. The tool (711) may be sensitive to static magnetic fields or electromagnetic waves and may be used to detect the presence of the generated magnetic particles.

The sensing applications may utilize the increase in effective magnetic permeability of the fluid due to the presence of magnetic particles. Non-limiting examples include electromagnetic surveying, nuclear magnetic resonance utilizing the plurality of generated particles as a contrast agent, magnetophoretic pressure sensing and thermal measurements on inductively heated particles. Flow control applications which use the generated particles can take advantages of the magnetic field dependent transport properties of the fluid, in non-limiting examples viscosity or yield stress.

While the subject disclosure is described through the above exemplary embodiments, it will be understood by those of ordinary skill in the art that modification to and variation of the illustrated embodiments may be made without departing from the inventive concepts herein disclosed. Moreover, while the preferred embodiments are described in connection with various illustrative structures, one skilled in the art will recognize that the system may be embodied using a variety of specific structures. Accordingly, the subject disclosure should not be viewed as limited except by the scope and spirit of the appended claims. 

1. A method of generating magnetic particles in a wellbore comprising: introducing a fluid system into the wellbore comprising a first fluid and a second fluid; and reacting chemically the first fluid and the second fluid in the wellbore to form a plurality of magnetic particles.
 2. The method of claim 1 wherein the plurality of magnetic particles are magnetically attracted to one another in response to exposure to a magnetic field.
 3. The method of claim 1 wherein the first fluid comprises one or a plurality of irons salts.
 4. The method of claim 3 wherein the one or the plurality of iron salts comprises at least an iron (II) salt and an iron (III) salt.
 5. The method of claim 3 wherein the iron (II) salt is selected from the group consisting of: iron (II) chloride tetrahydrate, iron (II) sulfate heptahydrate, iron (II) sulfate hydrate, iron (II) oxalate dehydrate, and combinations thereof.
 6. The method of claim 3 wherein the iron (III) salt is selected from the group consisting of: iron (III) chloride hexahydrate, iron (III) nitrate nonahydrate, ion (III) sulfate hydrate; iron (III) oxalate hexahydrate, and combinations thereof.
 7. The method of claim 1 wherein the plurality of magnetic particles are iron oxide particles.
 8. The method of claim 7 wherein the iron oxide particles are magnetite or maghemite.
 9. The method of claim 1 wherein the second fluid comprises hydroxide ions.
 10. The method of claim 9 wherein the hydroxide ions are selected from the group consisting of: sodium hydroxide, potassium hydroxide, barium hydroxide, strontium hydroxide, calcium hydroxide, lithium hydroxide, rubidium hydroxide, caesium hydroxide or ammonium hydroxide and combinations thereof.
 11. The method of claim 1 wherein the second fluid is a cement slurry.
 12. The method of claim 1 wherein the first and the second fluid are non-magnetic.
 13. The method of claim 1 wherein a dispersion of the plurality of particles is sufficient for at least one use selected from the group consisting of: downhole sensing or downhole flow control.
 14. The method of claim 1 wherein the plurality of particles are used in a downhole valve.
 15. The method of claim 1 wherein the plurality of particles are formed by co-precipitation.
 16. The method of claim 1 further comprising detecting the plurality of particles with a sensor in a well logging tool.
 17. A process for producing a plurality of magnetic particles comprising: introducing a fluid system into a wellbore comprising a first fluid and a second fluid; reacting chemically the first fluid and the second fluid in the wellbore; and co-precipitating a plurality of magnetic particles from said chemical reaction. 